Wells drilled in low-permeability subterranean formations are often treated by reservoir stimulation techniques, such as hydraulic fracturing, to increase their conductivity and thereby enhance recovery of hydrocarbons. Treatment fluids are pumped at high pressure into the formation to create fractures in the formation. Proppants may be incorporated in the treatment fluids to prop open the created fractures when the surface treating pressure is released. A wide variety of materials may be used for proppant, but it includes a solid material, often sand or ceramic particles.
In “hybrid” fracturing procedures, different fracturing fluids may be implemented to accomplish various stages of formation fracturing and proppant placement. A job may begin with a slickwater fracturing stage, or several slickwater stages, including a pad stage and early proppant stages. The pad stage fills the wellbore with the slickwater fracturing fluid. “Slickwater” refers to a treatment fluid with a comparatively low viscosity in the range of about 1 to less than about 5 centipoise (cP) at a shear rate of 511 seconds−1 (sec−1) and with a comparatively low concentration of proppant, such as less than or equal to about 3 pounds per thousand gallons (ppt), including the possibility of no proppant. Unless stated otherwise herein, viscosity values are for the materials at 20° Celsius (C). Despite the low viscosity, guar or derivatized guar without crosslinker may be present, but function as a friction reducer instead of a gellant material. In some hybrid jobs, one of the early stages may be left out.
Toward the middle of the job, during proppant stages, a linear gel fracturing fluid may be implemented for increased proppant transport and placement. “Linear gel” refers to a treatment fluid with an increased concentration of guar or derivatized guar without crosslinker to increase viscosity to the range of about 5 to less than about 50 cP at 511 sec−1 and with greater than about 2 ppt of proppant. Later, a crosslinked gel fracturing fluid may be implemented for a still further increase in proppant transport and placement. “Cross-linked gel” refers to a treatment fluid with a crosslinker to increase viscosity to the range of about 50 cP and higher at 511 sec−1, such as to about 2,000 cP, and with greater than about 3 ppt of proppant. The guar or derivatized guar may be crosslinked for such treatment fluid.
Research and development has included finding viable alternatives to guar-based polymers due to cost and availability. Accordingly, polymers suitable as guar replacements are desirable.